EF导航属性更新

Question

Sorry for my bad English.

I have some class and EF Context generate from DB

1.Question

public int Id { get; set; }
public string Content { get; set; }

public virtual ICollection<Answer> Answer { get; set; }

2.Answer

public int Id { get; set; }
public string Content { get; set; }
public bool IsTrue { get; set; }

public virtual Question Question { get; set; }

All CRUD made through the Service. This is Update method for Question

public void Update(Question q)
{
   var editQuestion = GetById(q.Id); //get entity by id
   editQuestion.Answer = null;
   _repository.Update(editQuestion);

    q.Answer.Each(answer => answer.Question=editQuestion);

    editQuestion.Answer = q.Answer;
    editQuestion.Content = q.Content;

   _repository.Update(editQuestion);
   _unitOfWork.Commit();
}

_repository.Update(T Entity) =>

public virtual void Update(T entity)
{
   DbEntityEntry entityEntry = _context.Entry<T>(entity);
   entityEntry.State = EntityState.Modified;
}

Now in Db not update old Answer, but added new (q.Answer). In q.Answer may contains updated old Answer and some new.

How I can update Question?

UPD: _unitOfWork.Commit()

public void Commit()
{
   _context.SaveChanges();
}

Answer 1

There is no need to play with the entry state. Simply get the entity by its Id, modify the relevant properties, remove old answers from the context, add the new ones to the collection, call SaveChanges() and it's job done.

Typically, one would write something like:

public void Update(Question q)
{
  using(var context = new MyDbContext())
  {
    var entity = context.Question.Find(q.Id);
    entity.Content = q.Content;

    foreach(var oldAnswer in entity.Answer)
    { 
      context.Answers.Remove(oldAnswer);
    }

    entity.Answer.Clear(); 

    foreach(var newAnswer in q.Answer)
    {
      entity.Answer.Add(newAnswer);
    }

    context.SaveChanges();
  } 
}

If you are not using the using pattern, don't forget to dispose the context at the end by calling context.Dispose() .

Please note this is a solution where answer records would be deleted from the database and re-created even if they have not changed.

Alternatively, you could write a solution where existing records would be updated and only answers that no longer exist would be deleted:

public void Update(Question q)
{
  using(var context = new MyDbContext())
  {
    var entity = context.Question.Find(q.Id);
    entity.Content = q.Content;

    foreach(var newAnswer in q.Answer)
    {
      if (entity.Answer.All(a => a.Id != newAnswer.Id)
      {
        entity.Answer.Add(newAnswer);
      }
    }

    foreach(var oldAnswer in entity.Answer)
    { 
      if (q.Answer.All(a => a.Id != oldAnswer.Id)
      {
        context.Answers.Remove(oldAnswer);
      }
      else
      {
        var newAnswer = q.Answer.Single(a => a.Id == oldAnswer.Id);
        oldAnswer.Content = newAnswer.Content;
        oldAnswer.IsTrue = newAnswer.IsTrue;
      }
    }

    context.SaveChanges();
  } 
}